Effects of disc milling and indirect extrusion processing on mechanical properties of aluminum-graphene-composites with commercial GNPs

Abstract

Abstract. In this study aluminum-graphene-composites were manufactured applying a powder metallurgical approach. After graphene exfoliation and mechanical mixing, powders were disc milled, compacted and extruded into round rods. Two different sources of commercial graphene nano platelets (GNP) (by 1. Sigma Aldrich (SA) and 2. Alfa Aesar (AA)) were investigated with the main difference being their specific surface area. One subject of the study was to investigate the effect of disc milling processing on the mechanical properties of Al/GNP composites. Results indicated that micro hardness as well tensile yield strength (TYS) and ultimate tensile strength (UTS) were not improved significantly or only slightly when SA-GNPs and a disc milling duration of 1min were applied. Varying the extrusion ratio from R=9:1 to R=14:1 and R=31:1 as well as applying conic or flat face dies for extrusion did not have a significant effect on the mechanical properties. But when disc milling duration is extended to 5min, significantly increased micro hardness (up to 30%), TYS (up to 17%) and UTS (up to 26%) were observed. Application of AA-GNPs as a second source of commercial GNPs also resulted in significantly increased micro hardness (up to 49%), increased TYS (up to 16%) and UTS (up to 27%) when disc milling of 5min is conducted in the powder processing stage. SEM analysis indicated that after 5min disc milling aluminum particles were deformed from spherical into a plate-like shape. Additionally, GNP exfoliation and its dispersion in the Al matrix seemed to be improved by the longer milling duration and could be a reason for the enhanced strengthening effect of GNPs.